Ever since the invention of the telescope, people have been seeing weird things on the Moon. Paranormal packrat Charles Fort compiled lunar anomalies going back as far as the 18th Century.
More recently, weird stuff on the Moon has been dignified with a Three Letter Acronym: TLP, or Transient Lunar Phenomena. They exist in a kind of scientific "neutral zone," and attract attention from both serious astronomers and, well, crackpots.
Now one of the former group has come up with an interesting correlation between observed Lunar transients and episodes of radon gas emission on the Moon. This suggests that when people see strange spots and shadows on the Moon, plumes of erupting gas may be the culprit.
It's worth remembering how little we still know about the Moon. Sure, a dozen people have walked around on its surface and a dozen automated probes have landed on it or observed it from orbit. But the Moon is a world with as much land area as Africa. Humans have lived in Africa as long as there have been humans, and the continent still manages to surprise us. So it's no surprise that the Moon still holds plenty of mysteries.
Maybe someone should go back there and look around some more. Wouldn't hurt.